1. Technical Field
The present invention generally relates to methods of manufacturing a fluid dynamic bearing assembly. More particularly, the present invention generally relates to a method of manufacturing a fluid dynamic bearing assembly to enable the bearing-assembly shaft to be inserted into the bearing hole in a sleeve without scratching the inner circumferential surface of the sleeve or the outer circumferential surface of the shaft.
2. Description of the Related Art
In manufacturing the bearing assembly including a shaft and a hollow sleeve having a bearing hole, axially penetrating the sleeve, the shaft needs to be inserted into the bearing hole from one end opening toward another end opening. To insert the shaft into the bearing hole, a conventional assembling machine of the bearing assembly, shown in FIG. 7, may be used.
As shown in FIG. 7, the conventional assembling machine includes a sleeve cradle 101 supporting the sleeve 3, a vacuum line block 102 fixing the sleeve 3 and the sleeve cradle 101 by vacuuming up, a shaft insertion guide 103 having a guide hole 103a leading the tip end of the shaft 4 into the bearing hole 3a provided on the sleeve 3.
Moreover, the sleeve cradle 101 includes a plurality of suction holes 101a vacuuming up and fixing the sleeve 3. The vacuum line block 102 includes a vacuum line 102a. In addition, an airpool portion 102 is provided between the sleeve cradle 101 and the vacuum line block 102. The vacuum line 102 is connected to a vacuum forming machine (not shown in Fig.) through a vacuum line 105 whose one end is connected to the vacuum line block 102, another end is connected to the vacuum forming machine.
The conventional assembling machine with the configuration mentioned above vaccumizes the airpool 104, the suction hole 101 a, the vacuum line 102, and the vacuum line 105, such that the sleeve 3 is aspirated and fixed to the sleeve cradle 101. Subsequently, insertion guide 103 is adjusted so as to lead the shaft 4 into the guide hole 103a. Under the condition, the shaft 4 is inserted into the bearing hole 3a through the guide hole 103a of the shaft insertion guide 103 (see FIG. 7A).
Upon inserting the shaft 4, a position of the shaft insertion guide 103 is adjusted by an actuator, such as a motor, to align a center axis of the guide hole 103a and a center axis of the bearing hole 3a. In order to insert the shaft 4 into the bearing hole 3a with the shaft insertion guide 103, the center axes of the guide hole 103a and the bearing hole 3a need to be precisely aligned. In other words, the shaft insertion guide 103 needs to be highly precisely adjusted.
On the other hand, there is a clearance between the shaft 4 and the bearing hole 3a, and a tip end of the shaft 4 been inserted into the bearing hole 3a may incline corresponding to the clearance. In order to prevent the shaft from inclining, the vibration along an X direction shown in FIG. 7b is applied to the vacuum line block 102 with an actuator such as a cylinder (not shown in Fig). With aligning the center axes of the shaft 4 and the bearing hole 3a by applying vibration along the X direction in predetermined times, the shaft 4 is inserted into the bearing hole 3a, and then the insertion the shaft 4 into the bearing hole 3a is completed (FIG. 7C).
In the conventional manufacturing method, the outer circumferential surface of the shaft 4 and the inner circumferential surface of the sleeve 3 may contact each other, which may result in scratching the member with low hardness among the shaft 4 and the sleeves 3. For instance, if the hardness of sleeve 3 is lower than the hardness of shaft 4, the inner circumferential surface of the sleeve 3 is scratched. The sleeve 3 whose inner circumferential surface is scratched may influence the performance of the bearing assembly.